It’s the eighth most commonly prescribed drug in the U.S., with 52.3 million prescriptions written for it every year – many in winter for hacking coughs and suspected respiratory infections.

But amoxicillin, and its inexpensive generic equivalents, has been so overprescribed for bronchitis, it’s apparently no longer effective, a new study finds.

The study, published online this week in The Lancet Infectious Diseases, found amoxicillin (part of the penicillin family) no more helpful than a placebo in treating lower-respiratory-tract-infection symptoms – like a nagging cough and shortness of breath – or in preventing them from getting worse, Fox News reported.

“Patients given amoxicillin don’t recover much quicker or have significantly fewer symptoms,” coauthor Paul Little, M.D., of the University of Southampton in the U.K., said in a prepared statement. “Our results show that most people get better on their own.” Little said that overuse of antibiotics can lead to “side effects such as diarrhea, rash, vomiting and the development of resistance.”

The research follows a paper published in February in the Journal of the American Medical Association that found amoxicillin no better than a placebo at treating sinus infections.

Whether antibiotics can help older patients with respiratory illnesses has been hotly debated. Most of these chest infections are caused by viruses, which don’t respond to an antibiotic, but it’s hard for a doctor to determine whether a patient has a bacterial infection or a viral one. Often doctors prescribe an antibiotic just to be on the safe side, though these drugs can cause unpleasant side effects and may not even help the infection.

In the Lancet study, British researchers recruited 2,061 adult patients across a dozen European countries who had gone to their doctors for a lower-respiratory infection. All had a cough lasting under four weeks, but none were suspected of having pneumonia, Scientific American reported. Half the patients were given amoxicillin; half were given a placebo. Both groups were told to take their medication three times a day for seven days.

Doctors assessed each patient’s symptoms at the beginning of the study, and patients also kept a diary of each of their symptoms (cough, phlegm, headache, fever, etc.), rating them for severity from “no problem” to “as bad as it could be.” They also rated side effects – like diarrhea, vomiting or rash – for up to four weeks.

At the end of seven days the severity or duration of symptoms was nearly the same in both groups, researchers reported. Even among people 60 or older, who, compared with those who are younger, were thought to benefit more from antibiotics for infections, amoxicillin had minimal effect.

Symptoms rated “moderately bad” or “worse” lasted a median of six days in the group that took the amoxicillin, and seven days in the group that took the placebo. Slightly more patients taking a placebo had new or worsening symptoms – 19.3 percent versus 15.9 percent for those taking an antibiotic – but those taking amoxicillin had more side effects, like diarrhea, nausea and rash. Of the three people in the study who had to be hospitalized, two were taking antibiotics and one was taking a placebo.

An accompanying essay about the study by Philipp Schuetz, M.D., of the University of Basel in Switzerland, noted that the biggest hurdle to antibiotic use might be convincing patients and doctors not to overdo it. What physicians need, he wrote, is a quick blood test to indicate which patients have a bacterial infection, which antibiotics can treat, so patients with a virus can avoid the “toxic [side] effects” of drugs that probably won’t help them.

In other health news:

Study of aspirin-eye disease link finds weak evidence.A study that found an association between aspirin use and a form of age-related macular degeneration (AMD) does not prove that the common drug actually causes the eye disease, experts told National Public Radio. In the 10-year study of nearly 5,000 people in Wisconsin, about 1.76 percent of those who’d regularly used aspirin 10 years before a retina exam had signs of late-stage AMD, compared with 1.03 percent of those who hadn’t taken aspirin. But that doesn’t prove that taking aspirin caused the disease.

“Where have all the primary care doctors gone?” Pauline Chen, M.D., writing in the New York Times, says the shortage of primary care doctors – “general internists, family doctors, geriatricians and general pediatricians, the doctors responsible for diagnosing new illnesses, managing chronic ones, advocating preventive care and protecting wellness” – is expected to worsen in the next 15 years, which is bad news for an aging population.